1. Field of the Invention
The present invention relates to a smooth rod-gripping apparatus and, more particularly, to an apparatus including a housing for receiving a smooth rod, a plurality of elongated jaw members within the housing, and a force tube which secures the smooth rod within the housing by wedging the jaw members between the smooth rod and an inner wall of the housing.
In concrete construction, a cementitious material is placed between erected walls, termed formwork, which provide support until the curing process is completed. Tremendous force is often exerted upon the formwork, particularly when large volumes of concrete are placed. Tie-rods, termed formties, are passed through holes drilled in the formwork and secured in position relative to the forms to prevent an outward expansion of the erected forms during the placement and initial hydration, set, of concrete walls.
The formwork typically includes beams, planks, or the like ("wales" and "stiffbacks," as known in the construction trade). A rod-gripping apparatus is used to prevent the formwork from sliding outwardly along the formtie. The formwork, in turn, serves as a guide for the formtie and as a platform against which the rod-gripping apparatus is positioned. The force-distributing construction of the formwork supports the erected walls and prevents outward bulging of the walls while the wet concrete is curing.
Although concrete construction techniques have progressed tremendously in the last 50 years, most form ties have not changed. The use of steel ties is particularly problematic because of the need to avoid rust which can destroy a structure or ruin its appearance. Prior attempts to eliminate structural rusting include either entirely removing the steel rod or breaking the rod back below the surface. The resulting hole is then plugged and patched over with cementitious material. These practices are very labor-intensive and expensive. Unfortunately, the patching often results in an unprofessional finish, or worse, is overlooked, or simply fails to prevent rusting from occurring.
The smooth rod-gripping apparatus disclosed herein is beneficially capable of gripping smooth fiberglass rods, thereby eliminating the problem of structural failure due to steel formtie corrosion. Furthermore, the rod-gripping apparatus, which includes a unique jaw cluster mechanism, does not need to be "preset" to compensate for anticipated slippage as is required with presently-available rod-gripping devices.
2. Description of Related Art
The art of rod-gripping devices is generally cognizant of gripping devices specifically designed for use with threaded rods. Camming mechanisms used to secure a rod within a gripping device are also known. Representative prior art in the field of rod-gripping devices is included below.
U.S. Pat. No. 4,192,481 discloses grippers that are specifically designed for use with a threaded rod, and not a smooth rod. U.S. Pat. No. 2,614,801 discloses a wire-holding and prestressing device.
U.S. Pat. No. 3,910,546 teaches a she-bolt-type gripper device for a concrete wall formed tie rod. U.S. Pat. No. 3,965,542 is similar to the preceding reference, and further adds a latch mechanism.
U.S. patent application Ser. No. 1,634,422 discloses a rod clamp which operates by camming the tabs of opposing grip members within spiralled slots. U.S. Pat. Nos. 2,075,239 and 2,171,120 both teach variations of a tie wire mechanism.
U.S. Pat. No. 2,699,589 discloses a smooth rod clamping device. U.S. Pat. Nos. 2,896,496 and 3,117,485 teach the use of a spring within a shaft clamping mechanism. U.S. Pat. Nos. 4,192,215 and 4,363,462 are additionally cited as of interest.
The need for an improved smooth rod-gripping apparatus for securing formwork to a formtie still exists. When two opposing forms are erected to form a channel into which concrete is placed, they must be held together until the concrete sets. A rod is passed through the formwork which is positioned on the outwardly-facing surfaces of the structure to be constructed. The formwork, through which the rod passes, serves as a base or platform for a rod-gripping device. A problem typical of smooth rod-gripping apparatuses is that slippage occurs, allowing the walls to expand. Various presetting techniques, such as pounding a wedge-shaped object between the gripping device and the formwork, have been utilized in attempts to minimize this slippage. The inclusion of springs in many existing smooth rod-gripping devices contributes to this slippage.
Another problem typically associated with smooth rod-gripping devices is that formties can only be inserted into one end of the device because of the action of various springs which prevent entry of the formtie from either end of the gripping device.
The smooth rod-gripping apparatus disclosed herein effectively secures smooth rods comprised of metallic or nonmetallic (i.e., fiberglass) materials within the apparatus' housing. The apparatus includes a housing and a plurality of gripping members which are wedged between the outside of the rod and the housing's inner wall, thereby securing the rod within the housing. The smooth rod-gripping apparatus is comprised of very few parts and includes no springs.
Since the disclosed smooth rod-gripping apparatus is designed to grip fiberglass and other smooth rods, the above-discussed problem of structural rust is completely eliminated.
The disclosed apparatus additionally includes a release mechanism which allows the rod-gripping apparatus to be slid off the rod after the rod is cut flush with the wall. Hence, the smooth rod-gripping apparatus is reusable. Alternatively, the release mechanism permits the rod-gripping apparatus and the formwork to be slid off the rod, after which the rod may be cut flush with the wall.
Although several formtie clamping devices exist, the art is still without an inexpensive, smooth rod-gripping apparatus which consists of very few parts and no springs, requires no presetting, grips nonmetallic rods, and releases from the rod for reuse.